Not Applicable
Not Applicable
The field of the invention relates generally to the utilization of electric power, and specifically to a device that can remotely curtail the electric demand of a premises during supply shortages and periods of high power prices.
The two primary components of electric bills are energy charges and demand charges. Energy is the amount of the commodity of electricity consumed, and it is measured in kilowatt-hours (kWh). Demand is the rate (that is, the pace) at which energy is consumed, and it is measured in kilowatts (kW). Demand charges are computed from the largest average demand of a sequence of equal time intervals, usually 15 minutes long. Both energy charges and demand charges can vary by time of use.
Deregulation of the electric utility industry has been accompanied by the emergence of spot markets for electric power and access to those markets by utility customers. Since electricity cannot be stored on a large scale, energy prices tend to be highly dynamic over time scales as short as a day. Most markets post prices hourly, every 15 minutes, or even oftener. Some electric suppliers have implemented Real-Time Pricing (RTP) under which prices are posted when, or shortly before, they become effective. Under RTP customers can reduce their electric bills by shifting usage from periods of higher to lower prices. This strategy has three prerequisites: (1) a method to communicate energy prices (2) ability to control the customer""s lighting and electric equipment so as to shift or curtail usage, and (3) a method of verifying the response, usually by employing a so-called interval meter that records electric usage as a function of time. RTP has a secondary benefit in that price response on a large scale can take some of the pressure off the power markets and reduce price volatility.
For many years utilities have offered interruptible electric rates, which provide a discount in return for customers agreeing to interrupt service during power shortages. The shortage may arise suddenly if a large generating unit breaks down, and action must be taken within minutes to prevent the collapse of the power grid in an entire region. After a decade or more without an incident, interruptible rates were put to the test in California during the power shortages of the summer of 2000 and the following winter. Many interruptible customers elected to pay stiff penalties rather than shutting down their facilities. Customers who did shut down sent thousands of workers home, lost production and incurred significant economic losses. Utilities also implemented rolling blackouts during this period. Curtailment, that is, an orderly, predictable demand reduction is more palatable and less disruptive than these drastic measures.
Commercial and industrial utility customers have embraced the energy management system (EMS) as an effective way to lower their electric bills. Most of the systems in service work autonomously and limit demand. They sense demand in one of several ways. Most commonly, the electric meter is fitted with an accessory that produces pulses, which are called xe2x80x9cKYZxe2x80x9d pulses by the electric utility industry. A pulse is sent each time a certain amount of energy is metered, and the rate at which the meter sends pulses represents the current demand. When the demand (that is, the pulse frequency) exceeds a programmed limit, the EMS responds by switching off one or more pieces of equipment and/or changing process set points. An example of the latter is that an EMS would turn a thermostat a few degrees higher on a hot afternoon to curtail the power consumed by an air conditioning system. The electric meter may instead communicate demand in the form of an analog signal or serial data, but the principle remains the same.
In concept it is possible to develop a device that reprograms an EMS dynamically in response to RTP rates or to curtail demand. There are many types of EMSs, and they employ many different programming languages and communication protocols. Electric rate structures vary from one locale to the next. Most importantly, each EMS is programmed individually for the particular equipment and premises it serves. Therefore, each such device would have to be custom-programmed for each EMS, and the associated cost would be restrictive, if not prohibitive.
Many types of EMSs have been developed, and they are in widespread use. U.S. Pat. No. 4,324,987 to Sullivan, II, et al. (1982) describes an autonomous EMS that limits demand by controlling discrete electric loads. However, this system and the vast majority of EMS designs in service today have no communication pathway that enables either RTP response or remote curtailment capability.
U.S. Pat. No. 6,327,541 to Pitchford, et al. (2001) provides centralized access to electric usage data from a multitude of locations. While the patent is entitled xe2x80x9cEnergy Management Systemxe2x80x9d, the claims do not cover the control of energy end-uses.
U.S. Pat. No. 5,502,339 to Hartig (1996) describes an EMS that controls end-uses. In concept, it can curtail demand and respond to RTP, but it accomplishes this by the slow and awkward procedure of reprogramming the EMS over a telephone line. The method described is not practical for thousands of customers who may have to respond in a timeframe of minutes.
U.S. Pat. No. 5,572,438 to Ehlers, et al. (1996) describes an EMS that is accessible and controllable from a central location. Conceivably the EMS could provide price response, but the claims don""t cover this capability. Implementing this system would require the installation of a sophisticated controller, as well as control hardware in each branch circuit to be controlled. In other words, this patent describes an entire EMS, which would be expensive, although it would provide functionality and potential cost savings beyond the typical, autonomous EMS. U.S. Pat. No. 5,696,695 also to Ehlers, et al. (1997) describes explicitly an EMS that is responsive to energy prices. As in the previous case, implementing this system would require installation of an entire EMS at substantial cost.
U.S. Patent Application 20020019758 by Scarpelli (2002) describes a xe2x80x9cload management dispatch system and methodxe2x80x9d and presents some 61 independent and dependent claims for xe2x80x9cmethodsxe2x80x9d and xe2x80x9csystems.xe2x80x9d The only claim that relates to control of end-uses is (dependent) claim 58, which states: xe2x80x9cthe signal is operative to automatically initiate a load curtailment by the energy consumer.xe2x80x9d The specification adds no specificity to the embodiment of xe2x80x9cload curtailment.xe2x80x9d The broad description in the cited application is ripe for the development of well-defined, workable inventions that incorporate control of end-uses. If one assumes the embodiment of Scarpelli""s application includes a full EMS, significant cost will be incurred to implement it and to establish the required communication pathways.
U.S. Pat. No. 4,819,180 by Hedman, et al. (1989) describes a method and system for regulating power delivered to commercial or residential users. When the electric utility transmits a control signal to a user, a variable limit demand controller modifies the power consumed by the user. It does so by modifying a stored demand limit and switching electric loads on or off to attain the modified demand limit. While it is possible to implement Hedman in the stocks of existing EMSs, doing so would require that each EMS involved be individually reprogrammed to modify and seek the modified demand limit during curtailment events. If large numbers of EMSs are involved, reprogramming becomes a daunting and costly task due to the many different protocols, programming languages, program structures, and physical programming interfaces that must be dealt with. Further complicating this task is that each facility has its own mix of electrical loads and control requirements.
Hedman discloses a utility control signal that is binary-on or off, and a single percentage demand reduction that resides in the controller""s non-volatile memory. Thus, Hedman is limited to curtailing by a fixed percentage, unless the memory is reprogrammed at the site.
The salient question is how to cost-effectively tap the potential of the existing stock of EMSs, which control a significant amount of demand grid-wide. If this can be done cost-effectively, these EMSs can be employed to provide RTP response for individual customers, as well as grid-wide demand curtailment during supply shortages. Prior art does not provide the answer.
Objects and Advantages
The device for curtailing electric demand provides customers who utilize energy management systems (EMSs) a cost-effective method of responding to real-time pricing (RTP) of energy. Furthermore, the device allows the customer to be curtailed within one minute of sending a command from a central location. Widespread implementation of the device can mitigate the need for disruptive rolling blackouts and power interruptions.
Prior art can provide these capabilities by installing a complete, state-of-the-art EMS. This will generally incorporate a sophisticated controller, which may have hundreds of inputs and outputs, a local network, cabling, and numerous load control components such as relays, starters, circuit breakers, contactors, etc. Furthermore, the new EMS must be programmed for the specific facility, and for the particular curtailment and RTP response strategies to be employed.
The key to the cost-effectiveness of the device for curtailing electric demand is that it provides these capabilities by harnessing the intelligence of existing EMSs. Furthermore, the device utilizes existing infrastructure to provide a low-cost communications pathway for EMSs lacking that feature. In contrast to prior art, the device is a relatively simple and is much lower in cost. Furthermore, the device""s unique principle of biasing the demand signal to the EMS takes advantage of the existing programming in the EMS, and eliminates the need for costly reprogramming. Therefore, the costs of new hardware and installation are minimized.
A wireless pager service provides a viable communication pathway for the device for curtailing electric demand, so no wiring to an external network is required, nor is a local network. The content of the curtailment commands is simple and direct, consisting of a curtailment level, a start time, a stop time, and an address. Certain pagers and paging services can handle broadcast messages, permitting large numbers of customers to be curtailed by a single command. This capability makes the device especially suitable for use during supply shortages when many customers must be curtailed quickly. Still further objects and advantages will become apparent from a consideration of the ensuing description and drawings.
The device for curtailing electric demand is suitable as a tool for responding to the real-time pricing of electrical energy, or for reducing demand during power shortages. Typically, a computer in a central location would issue curtailment commands to the device through a wireless communications network, but a wireline or optical network could be used instead. The device works in conjunction with an energy management system (EMS), which receives demand signals from an electric meter. In common practice, EMSs are programmed to limit electric demand, and the device takes advantage of that strategy. Upon executing a curtailment command, the device intercepts and biases the signal going to the EMS, which, in effect, coerces the EMS to reduce the demand upon the meter, and upon the electric grid.